


Humanity's Greatest Warrior

by LPSunnyBunny



Category: Harry Potter - J. K. Rowling, Shingeki no Kyojin | Attack on Titan
Genre: Canon-Typical Violence, Cross Dimensional Summoning, Eren Jeager is Dangerous As Shit, Gen, The Wizarding World is Not Prepared, magical slavery
Language: English
Status: In-Progress
Published: 2019-08-07
Updated: 2019-08-07
Packaged: 2020-08-11 02:06:22
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 3,144
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/20145790
Author URL: https://archiveofourown.org/users/LPSunnyBunny/pseuds/LPSunnyBunny
Summary: Eren Jaeger is ripped across time and space by Lord Voldemort. This proves to be a mistake. Adeadlymistake.Really, Lord Voldemort should have known better.





	1. Prelude: Intrusion

_ “Severus… Give it to me.”  _

_ “Yes, my lord.” A pale hand, reaching out expectantly. A twisting crystal, placed into a palm. A circle, detailed and intricate on the floor. Triangles and shapes and grooves carved into the smooth grey surface. . _

_ “Excellent.” Holding the stone up to his eyes, he examined it, watching the torchlight play off the strange curves and jagged edges. “And you are sure this is it?”  _

_ “Yes, my lord.”  _

_ He laughs, high pitched and cold. “Then let us perform the ritual without delay. The warrior awaits.” _

_ Magic, surging through his veins. The crystal dropping to the floor and shattering as magic poured into it, the circle starting to glow. Chanting. Foreign and dangerous. It surged up to the boiling point, gleeful, as a shape started twisting into existence, dark shadows and burning, piercing green eyes, wide and demented. A being staggering to its feet, eyes fixed on his own, soon the most powerful warrior through all of time would be  _ ** _his-_ **

Harry surged awake, his scar burning, a shout trapped in his throat. His hands shook, palms damp as he scrambled out of bed, fumbling for his glasses. Like all visions, it was immediately starting to slide away from him, dripping through his fingers like sand. He shoved his glasses on, blinking into the dark of his room for a moment, illuminated only by the streetlamps outside, before squeezing his eyes shut, trying to catch the remainder of the dream.

Voldemort had been pleased. No, he had been  _ ecstatic _ . Something was happening- something that he had been working towards. Something dangerous. A weapon, or- or- 

A  _ warrior.  _ Voldemort had been trying to summon a warrior. Harry all but threw himself across his room to his rickety desk, scrambling for a piece of parchment. 

_ Snuffles-  _

He paused, ink dripping from his quill. How on earth was he supposed to word this? He had to be careful with his words, the letters from his friends all summer oozing with the need to press the need for secrecy onto him. 

_ Snuffles- _

_ I’m dreaming again, you know about who. He was happy. It hurt. In the dream, he was almost trying to… I don’t know, summon something I guess. Some kind of ultimate fighter or warrior or great person. It’s fading, but it felt… dangerous. I can’t remember too much. Nightmares always go fast, right? This one feels like it’s going to linger. Like it’ll have a real lasting effect, if you know what I mean. _

_ But I guess it was just a dream. It doesn’t really matter that much in the end, right? Hopefully it’s not some kind of bad omen. _

_ Wish you were here. The Dursleys are being horrible as usual, so nothing new on that front.  _

_ -Harry _

He set it aside for a moment to dry. Hedwig had perked up the moment she saw he was writing a letter and he rose to his feet.

“Hey girl.” He said softly, holding out a finger to her. She nipped it affectionately and he slowly ran his fingers down her back, over her soft feathers. “Got a letter for Sirius for you. Wait for a reply, okay?” 

She hooted softly in affirmation. He bundled up the now-dry letter and tied it to her leg, offering her his arm. She hopped onto it and preened his hair as he brought her over to the window. He opened it and let her fly out. 

Harry watched her vanish into the night sky. He felt too awake, too wired to fall back asleep, so instead he reached for his textbook, intent on getting a little work done. His scar prickled and he rubbed at it, wincing slightly. It felt like it was going to be a long night.


	2. Stranded

Eren, Mikasa and Armin were sitting together on a set of crates in a side room, quietly preparing for the upcoming excursion into the territory of Wall Maria. Quiet, yet determined, conversation passed between them, just waiting for the time for them to depart. 

The three sixteen year olds were battled hardened, each of them having managed the accomplishment of lasting a full year of war against the monstrous titans that roamed the land they were fighting to reclaim. Their bond had been forged harder than steel, each of them covering each other’s weaknesses easily and coming out all the better for it.

Armin, the physically weakest but intellectually strongest, ready to devise tactics and direct the other two. Blond and short, he was often underestimated, but time and time again he had proven his mettle.

Mikasa, the one with the sharpest instincts and best fighting ability, ready to cover for any slip ups the other two might make. Heralded as the strongest fighter of their generation, she carved through titans like they were nothing. 

And Eren, the titan shifter that could decimate titans by the dozen. His determination burned darker and stronger than any other soldier, always getting back up no matter what. He often had to have his recklessness curbed by Armin and Mikasa, but nobody could deny his strength of will.

Mikasa and Armin were quietly discussing their positioning in the upcoming expedition, only for them to shoot to their feet as Eren gave a startled shout. Pain was spiking up his feet as thick black smog burst out from around his feet. 

“Erin?!” Armin gasped, confused. The smoke wasn’t anything like when Eren usually transformed into a titan, usually then it was a crackle of thunder and an explosion of lightning. 

“Shit- fucking-” Eren gasped, stumbling to his feet. Mikasa caught his shoulders, streadying him, eyes narrowing as she looked at the smog.    
  
“Armin, get Levi!” She ordered. “Something’s wrong!” 

Armin bolted for the door, vanishing down the hallway. 

“Fuck! It fucking hurts!” Eren gasped through gritted teeth, leaning heavily on Mikasa. “What the fuck is going on?!” 

“I don’t know- stay with me Eren.” Mikasa said, her eyes flicking rapidly from his face, down to his feet, where the smog was growing, traveling up his legs, devouring him. “Focus on me.”

Eren tried to focus, he really did. His head was starting to pound, the pain reaching into his chest. “Shit- shit! Shit!” He gasped, his knees going wobbly as they disappeared into the smog. 

“Don’t you leave me, Eren.” Mikasa demanded, holding his hand tight even as Eren gave a sharp hiss of pain. “Don’t give in to whatever this is.”    
  
“Fuck-” His grip went tight on Mikasa’s forearms. “It’s like I’m being doused in ice and set on fire!” 

“Eren!” Armin shouted, bursting back into the room, Levi and Hanji running in after him. 

“Eren!?” Hanji gasped, her eyes going wide. 

“Hanji, Levi-!” Mikasa’s gaze snapped over to the two of them, before darting back to Eren. The smog had reached his chest. “Help him!” She demanded.

“I don’t even know where to begin!” Hanji shot forwards, grabbing Eren’s shoulder. “Is this some kind of shifter side effect? Is his form destabilizing somehow?” She pressed one foot into the smog, only for it to go clean through, as though Eren’s legs were no longer there. 

“A little- haste would be appreciated!” Eren forced through gritted teeth, his head spinning. It was like there was a double layer over his eyes, the room and people around his going transparent like a pane of glass, another space filling in over them. Grey concrete, two figures standing, sickly green light.

“Eren-  _ Eren?! _ ” Mikasa’s voice was growing desperate. Her touch vanished, her hands sliding right through him.

“Mikasa-!” Eren fell to his knees, no longer held up by her strength. 

_ “EREN!”  _ The shouts were ringing in his ears but the room was dissolving before his eyes, like he was seeing double. He curled in on himself as his entire body was wracked with pain, cobbled floors under him overlaid with a smooth concrete, strange symbols coming into existence on the floor. He looked up and met burning red eyes.

They were magnetic, hypnotic, almost. Burning red in a strange, white face, flat and snakelike. Eren felt pinned in place, Mikasa’s begging ringing in his ears even as it faded. 

_ “Eren, please, don’t go- don’t leave me- Eren-!”  _

His vision stabilized into the new space and he immediately categorized everything around him. A small room, almost claustrophobic in its size. Two men standing before him, the white-faced man and one other, tall with long black hair. 

The white-faced man spread his arms wide, stick held in one hand, and said something, possibly some kind of greeting. Eren stared at him for a moment, his confusion ebbing into a kind of rage. Whatever had happened to him, whatever strange event that had brought him here, this man had something to do with it. 

“Who are you?” He asked, pushing up to his feet, fury sparking through him. “What did you do to me?!” He demanded. 

The man paused, before he brought the stick to his throat and lightly tapped it, saying a word, before addressing Eren. “Can you understand me?” He asked, burning red eyes fixed on Eren’s luminescent green ones. 

“Yes.” Eren said shortly, shifting slowly on his feet. He took a moment to thank the fact that they had all been on standby when this happened, his 3DMG was currently strapped to his hips. Not that it would be much use in this close of a space, but he at least had a weapon in the form of his blades. 

“Good. My name is Lord Voldemort.” The white-faced man said. “I have summoned you.” There was a strange smile on his face, like someone trying to be amicable while also hating the other person’s guts. Eren saw it all the time on Jean’s face whenever he was trying to be nice to Eren around Mikasa.

“Summoned?” Eren demanded. “What the fuck is that supposed to mean?”

“You are the greatest warrior in existence.” Lord Voldemort said. “I have summoned you here to assign you a task.” 

“What the fuck do you mean,  _ assign me a task?”  _ Eren snapped, losing his (admittedly short) patience. He drew his blades, pointing one at Lord Voldemort, ignoring the way the black-haired man pointed his stick at Eren in response. “You better unsummon me right now!” 

Eren’s mind was whirling even as he spoke. Summoned? Like a military summons? What on earth was he talking about? Whatever this  _ Lord Voldemort  _ had done, that was- it was almost like magic. And what the hell did he mean “greatest warrior in existence”? Admittedly his titan form was pretty incredible and powerful, but the title of “humanity’s strongest” should go to Levi, or the “greatest warrior” would be more up Mikasa’s alley!

“Oh, don’t worry.” Lord Voldemort made a pacifying gesture. “By summoning you, a contract has been created. The moment you complete your task, I will send you back.” 

Eren stared Lord Voldemort down, along the line of his blade. “Bullshit.” He said. “Whatever you did, you can reverse it. So unsummon me.”

“No can do.” Lord Voldemort said smoothly. “You must accomplish whatever task I put to you before the contract is completed.”

“Right.” Eren’s hand clenched his blade tightly. “Or maybe I’ll just take your head!” He shot forwards his blade coming up, starting into a spin to take this  _ Lord Voldemort’s  _ head. 

“ _ Immobulus.”  _ Lord Voldemort drawled and Eren felt himself freeze in place, all momentum halted immediately. “What a shame. I suppose we shall have to do this the difficult way.” 

Eren didn’t understand what was happening. He couldn’t move an inch, even as his body continued to breathe. At most he could flick his eyes, watching furiously as the black-haired man stepped forwards, gesturing with his stick. His body  _ lifted off the ground.  _

He was  _ floating.  _

Eren felt his mind make a valiant attempt to shut down, and only through sheer force of will kept it working. 

Right. So whatever the fuck was going on here, it was clearly not anything he had ever enounctered before. They were casually breaking the laws of reality like it was nothing. Doing impossible tasks. 

Were they witches? The Wallists had always denounced witches and heretics, magic users wanting to bring the walls down. Were they trying to get him to be a traitor to the Scouting Corps? 

His fury ignited at that, his struggle against his invisible bonds becoming twofold. With an almighty  _ wrench  _ he broke free, dropping to the floor with a wordless snarl. The black haired man gave a startled noise, but he ignored it, bringing his thumb up to his mouth. If these  _ bastards  _ wanted to turn him into a traitor, well, he would show them just how little they would be able to handle him! 

His titan form would be obvious and immediate, they wouldn’t be able to hide him away like they clearly intended to.

_ “Immobulus _ .” The man said hastily, and Eren felt himself freeze again.  _ Fuck you!  _ He silently snarled, trying to convey his meaning to the man with his glare. The man sneered at him before resuming the levitation, bustling Eren down the hall with a quicker pace before as Eren raged against his invisible bonds, struggling even harder. 

The man brought him into what was clearly a dungeon, and with a few gestures of the stick in his hand, Eren was divested of his equipment and forced back along the wall in a standing position. His arms were pulled out to his sides as chains  _ flew on their own  _ to clasp around his wrists. 

Then he was released from his immobility, and immediately began howling. “YOU BASTARDS! I’LL TEAR YOU APART, YOU FUCKERS!” He thrashed against the chains, trying to bring his hand within biting distance, but the chains didn’t give any grip. 

The black haired man stared at him impassively. Eren gave a snarl, jerking as far as the chains would let him go. He stared the other man down, knowing just how effective his furious glare could be, having heard reactions from the other members of the survey corps. 

The man met his stare easily, but Eren could see a level of caution appear in his gaze as Eren bared his teeth at him. Good. The moment Eren was free, he was going to tear his throat out with his teeth.

The man spoke a single word and Eren’s vision was consumed, his eyes rolling back in his head as memories were yanked to the front of his head.

_ He was being knocked on his ass again by Annie, the girl having flipped him easily. “Start using your head.” She said, her tone bored. “The more you just blindly charge at people, the more you’ll get beat.” _

_ Mikasa was looking down at him in concern. “Eren, you fell asleep again. We need to get the firewood back to mom.”  _

_ “I can’t believe you talked back to him like that!” Sasha gasped, half a loaf of bread in her mouth.  _

_ Titans, stepping through the broken wall. The sensation of transforming for the first time, desperate and furious.  _

_ “Mom- mom-!” Screaming as his mother was lifted up- _

** _No- _ **

_ “Run, Eren! You have to live!” Watching desperately- _

“GET THE FUCK OUT OF MY HEAD!” Eren roared, his head jerking back and slamming into the wall behind him, pain exploding into existence. The black haired man staggered back a step. 

At some point, Lord Voldemort had joined them, standing next to the black haired man. They spoke for a moment before Lord Voldemort stepped forwards, tapping his stick to his throat again.

“There is no need to fight if you would simply cooperate.” He said smoothly, likely assuming that Eren would be dazed and pliable for the persuading after the mental invasion.

Unfortunately for Voldemort, Eren was the type of person where pain made his thoughts clear and sharpen, instead of dull. He could feel his pulse settling, his thoughts clearing even with his mother’s screams ringing in his ears.

“Go to hell.” He said, and spat on the floor in front of Voldemort. “I don’t know what your schemes are, but I’ll have no part in them.” 

“What a shame.” Lord Voldemort said and stepped forwards, a grin spreading across his face as he raised his stick. “ _ Crucio.”  _

Eren’s world dissolved into pain. Stabbing through his bones, his blood boiling and frothing, a sharp, spiking thing that  _ didn’t stop.  _ It felt like he was getting flayed alive, like every muscle was slowly getting peeled back over and over. He screamed, thrashing back and forth against the chains holding him against the wall. 

Lord Voldemort held his stick up for a handful of moments more, before lowering it. The pain ebbed away, leaving Eren panting, breaking out into a cold sweat. 

“I am sure we can come to an agreement.” Lord Voldemort said then turned and swept away. He paused for a moment to speak to the other man in that strange language, then he was gone, vanishing down the hallway. 

Eren met the other man’s eyes, wordlessly snarling. He would kill them all.    
  
The man met his gaze and Eren was lost in memories again. He could feel the touch of the man carelessly rifling through his head, powerless to stop him. At certain points he could feel the man pulling some memories closer to the surface, forcing him to relive them. He seemed particularly interested in the memories of 3DMG training and the fighting against the titans, watching those memories a few times.

It wasn’t long before there was a strange sensation of  _ something  _ being dumped into Eren’s head, forcibly accommodating the new information. 

_ “Do you understand me?”  _ The man-  _ Severus Snape _ ,  _ potions master at Hogwarts- _ asked, the words strange and foriegn, but somewhere in Eren’s head they were translated.

Eren stared at him, clamping his teeth together. He understood immediately. Somehow, this- this  _ Severus _ man had planted information into his head, giving him a whole new language, and something else as well. 

_“Doo you understand me?” _Severus drawled again. He whipped his stick- _wand- _and a sharp sting slashed across Eren’s body _(a stinging hex)_, making him wordlessly snarl. He thought that would make him talk? He experienced worse in basic training! 

Severus clicked his tongue in irritation.  _ “Very well.”  _ He eyed Eren for a moment. “ _ I would think over your options carefully. Lord Voldemort is not a patient man. In time, if you do not agree… you may regret it.”  _

That said, he turned and swept out of the cell, his long black robes billowing out behind him. The cell door closed with a resounding-sounding  _ clang,  _ plunging Eren into darkness. 

Eren screamed in rage, thrashing against his chains. He just needed his hand, he just needed one bite that’s all it would take-

But no matter how he raged, his hands never moved more than a handful of inches from the wall.

**Author's Note:**

> If you like my work, check me out on [@LPSunBun](https://www.twitter.com/LPSunBun)!


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